It is California Presidential Primary Day in Los Angeles and the longest day of Federal Agent Jack Bauer's life is about to begin. Jack has just patched his family back together after a trying separation. Midnight finds Jack playing chess with his teenage daughter Kim. As she goes to bed, Jack gets a call from Nina Myers, his coworker at the Los Angeles Counter Terrorist Unit, telling him to come in for an emergency meeting. Jack has no choice but to report in, but he and his wife Teri learn that Kim has snuck out before he leaves.
Kim and her friend Janet York drive to an empty furniture store where they party with a couple of college guys whom they recently met. Kim enjoys herself at first, but starts to become suspicious of the two men when they won't take her home.
At CTU, Jack learns that an assassination attempt is being planned against Senator David Palmer; the first African-American presidential candidate with a serious shot at the White House. Jack's boss and friend, Richard Walsh, warns him that people in their own agency may be working with those who plan to kill Palmer.
Senator David Palmer is making his plans for Primary Day when he receives a strange phone call that puts him in a bad mood.
Jack shows how far he's willing to go to do his job when he blackmails District Director George Mason in the hopes of learning information about the Palmer hit.
Teri receives a call from Janet's father, Alan York, and the two decide to go out looking for the girls.
A European photographer makes pleasant conversation with a beautiful woman on a plane bound for LA. The two end up in a lustful encounter, but more sinister plans come to light that involve a stolen wallet and the destruction of the airplane.